There are just 30 candidates standing across the country who are not representing one of the big four parties.

Whittet, a company director and former journalist, registered his party on March 27 this year and had originally planned to build it up ahead of the Holyrood election scheduled for 2021.

It currently has a “handful” of members.

But Theresa May’s unexpected decision to go to the country provided him with an opportunity to contest the seat formerly held by Michelle Thomson, who was deselected as an SNP candidate last month.

“Here in Edinburgh West, the SNP is a soiled brand because of problems with their previous MP,” Whittet told The Scotsman. “They are most unlikely to hold the seat.

“I had written to Nicola Sturgeon asking her to stand down her candidate in the constituency because of the previous local difficulty.

“I plan to write to her again on June 9 asking for a progressive alliance ahead of the next Holyrood election.

Under a fairer, proportional representation system, the independence parties will offer two options rather than the three Unionist parties.”

Whittet, 58, believes the list format of Holyrood elections will benefit his party.

“At the moment, SNP supporters have no one to back with their second vote,” he said. “What I’m saying is, vote for the SNP on the fist ballot, and then vote for the Scottish Independence Referendum Party on the second.”

Asked if his party’s vote total would reach even three figures on Thursday, Whittet said “every vote counts and sends a message”.

He added: “The bigger picture is we can work with the SNP to build up an alliance. We share the common goal of putting Scotland first.”